A Review:Human Biological Adaptation to Artic and Subarctic Zones

Cold WinterThe main article summarized is Joseph Ko’s article Human Biological Adaptation to Artic and Subartic Zones.  This paper is a review of all literature pertaining to human climatic adaptation in the New World.    Most of the research subjects are Eskimo and artic Indian populations.  These groups are not often grouped together, but since both groups share similar physical conditions: extreme and prolonged cold; extremes of daily annual photoperiod; and low supporting biomass.  So makes sure to distinguish acclimatization from adaptation.    Adaptation is defined as an adaptive genotype that has emerged through the process of natural selection, while acclimatization on the other hand refers to genetic adaptation in which an adaptive genotype has emerged through the process of natural selection.  Also, So goes out of his way to point out the contentious nature of the current research in the field.

The current literature on human environmental adaptation places heavy emphasis on individual and population acclimatization to cold stress.  Many laboratory and field studies that have been performed involve the exposure of body parts (usually the extremities) to cold air or water or the exposure of the whole body to cold.  The first type of study usually compared the temperature responses of the extremities of native subjects with the responses of white, acclimatized controls, while the assessment of whole body cooling studies employed the use of equipment that help record physiological activity (BMR, deep body temperature, etc.).  Recent studies are more affected by Westernization, which is rapidly altering the diet, health, and general lifestyle of native populations.

There was correlation found between low environmental temperature and round headedness.  A rounder head offers the possibility for more efficient heat conservation; however later studies do not support these findings.  For example Steegman when he exposed Japanese and European subjects to environmental cold he found that supposedly “cold-adapted Mongoloid face” did not offer an advantage in maintaining warmer face temperatures.  Moreover, he found no other evidence in literature indicating the facial frostbite has been an important selective force in the course of human evolution.

Ethnographic evidence indicates that the Eskimo used their teeth to chew frozen sealskins and bones and as a vise in shaping implements. Such severe stress may have caused an increase in the size of the masticatory muscles, and a more anterior positioning of these muscles for more efficient chewing and biting. According to Hylander, this repositioning of the temporalis and masseter muscles is the cause of the typical facial flatness of the Eskimo. Human nose form has also been cited by a various authors in relation to climate.  One worldwide survey shows a correlation of +0.724 between mean annual temperature and relative humidity and the nasal index on the other. Essentially, as the climate gets warmer and more humid, the nose gets broader.

In cold-exposed individuals, the initial vascular reaction is vasoconstriction, the redirection of blood to the body core. This is often followed by a sudden vasodilation of the fingers or toes, resulting in rewarming of the extremity. After a period of rewarming, vasoconstriction sets in again. This cyclical pattern of cold-induced vasodilation and constriction (CIVD/CIVC) or “hunting response,” is often found among cold-adapted populations. The “hunting response” is advantageous because it decreases the likeliness of frostbite and cold injury while simultaneously avoiding excessive heat loss. So makes sure to point out the lack of comparability of earlier studies on Eskimo-Indian environmental physiology as a result of poor standardization of the methods.  So also does a wonderful job showing the contentious nature of human subartic adaptations studies, though I did not go into depth with all topics of debate if you want to find out more about the debated issues you should read the article.

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Demelio U.

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